Work machines, such as wheel loaders, excavators, and bulldozers, typically include a number of fluid cylinders such as hydraulic cylinders. Such hydraulic cylinders provide the motive power for moving components associated with the work machine relative to one another. For example, hydraulic cylinders may be used to move the lift arm of a wheel loader relative to the chassis.
Hydraulic cylinders typically include a housing having a piston which translates therein. A first end of a rod is secured to the piston and is extended out of and retracted into the housing as the piston is translated by changes in hydraulic fluid volume within the housing. It should be appreciated that a second end of the rod is secured to a component associated with the work machine so as to exert a motive force thereon. For example, the second end of the rod may be coupled to the lift arm of a wheel loader such that the lift arm is raised relative to the chassis of the wheel loader when the rod is extended out of the housing, and lowered relative to the chassis of the wheel loader when the rod is retracted into the housing.
In certain work machine designs, it is desirable to determine the position of the hydraulic cylinder. For example, it may be desirable to provide an "automatic lift" feature which lifts the lift arm of a wheel loader to a predetermined height and thereafter maintains the lift arm at the predetermined height. One way to determine the position of the hydraulic cylinder is to determine the location of the piston within the housing thereof. In particular, the location of the piston within the housing determines the amount of extension of the rod relative the housing which in turn determines the position of the lift arm relative to the chassis of the work machine.
Hence, a number of devices for detecting the location of the piston within the housing have heretofore been designed. Such devices typically have a number of drawbacks associated therewith. For example, such devices are generally mechanically and/or electrically complex thereby disadvantageously increasing costs associated with the work machine. Moreover, a number of such devices are disadvantageously affected by changes in both the pressure and temperature of the hydraulic fluid within the housing of the hydraulic cylinder. More specifically, a number of such devices have sensors which disadvantageously produce varying output signals as a result of changes in both the pressure and temperature of the hydraulic fluid within the housing of the hydraulic cylinder.
What is needed therefore is a method and apparatus for detecting piston location within a fluid cylinder which overcomes one or more of the aforementioned drawbacks.